Process for crimping multifilament yarn



Jan. 14,1969 .3. 1.. TAYLOR 3,421,193

PROCESS FOR CRIMPING MULTIFILAMENT YARN Filed March 31, 1965 Sheet of 2 I NVEN TOR Ji/vfsl [5)6406 Jan. 14, 1969 J. L. TAYLOR 3,421,193

PROCESS FOR CRIMPING MULTIFILAMENT YARN Filed March 31. 1965 Sheet 3 of 2 INVENTOR JZwzs L 174% 0,2

ATTORNEYS United States Patent 9 Claims ABSTRACT OF THE DISCLOSURE There is provided a process for crimping thermoplastic multifilament yarn and for increasing the cover factor and luster of said yarn. The yarn is passed between a pair of crimping rolls one of which is hard and heated to a crimping temperature, the other of which is composed of a substantially softer, yieldable material. The yarn is crimped while passing between the rolls and while the rolls have a pressure of at least 800 pounds per lineal inch. The yarn so produced has a series of permanent, non-uniform lateral loops equally spaced along a central, sinuous axis extending longitudinally along the yarn.

The present invention relates to the crimping of one or more ends of thermoplastic multifilament yarn in order to obtain a product having improved characteristics. In one important embodiment, the invention is concerned with method and means for continuously imparting a permanent and uniform crimp pattern lengthwise of a warp sheet of multifilament yarns While simultaneously displacing the axial relationship of the filaments in the individual yarn bundles. The thus processed yarns are useful in, for example, warp knitting although other uses and variations are also contemplated as will be hereinafter apparent.

Broadly stated, the method of the present invention involves passing one or more thermoplastic multifilament yarns between a pair of rotating crimping rolls, one of which is hard and inflexible, tag, a metal roll, heated to crimping temperature, and the other is composed of a substantially softer, yieldable material, e.g., rubber, and crimping the yarn between these rolls while exerting a critical roll pressure on the yarn.

The passing of a yarn or yarn sheet between two hard, intermeshing, rotating, heated surfaces in order to create a permanent linear deformation in a yarn or yarn sheet is a long established art commonly described as gear crimping. Various methods and apparatus of this general type are described in the prior US. patents (see, for example, 2,216,412; 2,575,833 and 2,988,799, among others).

It has also been proposed (2,668,430 and 2,668,564) to pass a plurality of monofilament nylon yarns between a metal gear or roll and another roll which, if desired, might be flexible or resilient. The purpose of such treatment is to dull the yarn and, to this end, the pressure between the metal gear and the companion roll (whether the latter is soft and flexible or otherwise) must be of relatively low magnitude (e.g., about 20 to 200 pounds per linear inch of roll face) in order to avoid filament flattening and obtain the desired dulling effect. The product obtained by the process described in 2,668,430 and 2,668,564 is characterized by a uniform number of regularly spaced sinuous bonds which are of substantially equal depth and are all located in a single plane running transversely of the roll axes. This single plane distortion 3,421,193 Patented Jan. 14, 1969 'ice holds true even if multifilament yarn is used in view of the low roll pressures which are employed in the procedures of 2,668,430 and 2,668,564.

In contrast to the above-noted prior techniques, particularly those described in 2,668,430 and 2,668,564, the present invention requires the use of substantial pressures between the rigid crimping roll and its flexible or resilient companion roll. Thus, for successful operation of the present invention, the roll pressure, i.e. the pressure on the yarn or yarn sheet during crimping, should be at least about 800 pounds per linear inch of crimping surface or roll face up to about 2,000 pounds or even higher.

Additionally, in contrast to the dulled product of 2,668,430 and 2,668,564 wherein the crimped monofilament yarn is only provided with a series of uniform bends in a plane transverse to the roll axes, the present product is characterized by increased luster and a series of permanent, irregularly spaced, non-uniform, minute lateral filament convolutions or loops essentially perpendicular to (i.e. in a plane essentially parallel to the axes of the rolls). These lateral loops extend outwardly from both sides of a series of substantially uniform sinuous bends which run lengthwise of the yarn in a plane generally transverse to the axes of the rolls.

Without being limited to any particular theory of operation, it appears that lateral filament displacements result from the squeezing action of the softer roll, single filaments in the yarn bundle migrating (because of modest yarn twist or other unknown factors) to form one or more laterally displaced loops of relatively low amplitude (e.g., 30 to 300 or more loops per inch of the product) first on one side of the yarn axis and then on the other. The number of such laterally displaced loops per inch appears to be constant for any given yarn and set of operating conditions. The exact number, however, appears to be dependent upon a variety of factors including: the number of filaments in the individual yarn bundle, the amount of twist in the yarn, the number of grooves per inch in the roll faces, the roll pressures used, the stitfness modulus of the yarn being processed, the relative differences in roll hardness, etc.

The invention is further described by reference to the accompanying drawings wherein:

FIGURE 1 is a perspective view of a system for processing multiple yarn ends or a yarn sheet according to the invention;

FIGURE 2 is a perspective view of one end of yarn processed according to the invention; and

FIGURE 3 is a perspective view of a method of using the yarn of the invention.

Referring more specifically to the drawings, FIGURE 1 shows a conventional warp beam 2 from which a plurality of multifilament yarns 4 are drawn in the form of a yarn sheet. These yarns are passed continuously and simultaneously between the crimping rolls or cylinders 6 and 8. Of these rolls, roll 6 may be made of steel, bronze or the like providing a hard and rigid surface for contact with the yarn. Roll 8, on the other hand, is made of a yieldable material such as rubber, compressed fibrous material or the equivalent. The two rolls may have matching transverse ridges and depressions although, preferably, for present purposes, the rigid roll is gear-shaped or otherwise provided with appropriate axial scoring, iluting or the like and the rubber or equivalent yieldable roll is plain surfaced as shown. In this way, by rotating the hard roll or cylinder which has been machined against the smooth, rotating surface of the softer cylinder and grad ually increasing the pressure between their faces, it is possible to imprint the surface of the softer cylinder with a pattern of lines or flutes exactly matching those which have been machined into the harder cylinder. Such a close matching of the cylinder surfaces is highly desirable as it facilitates the lateral displacement of the individual filaments from about the axis of each individual yarn during the crimping operation.

Roll 6 should be heated above the softening temperature of the yarn. To this end, suitable means 10 may be provided for feeding heating fluid through the roll although it will be appreciated that roll 6 may be heated in ways than by the fluid means as shown. The temperature to which roll 6 is heated will necessarily vary depending on other operating conditions, eg the type of yarn being processed, the rate the yarn is passed between the rolls, etc. However, the temperature should be adequate to soften the yarn and impart a permanent Crimp therein corresponding to the surface configuration of the rolls. Typical roll temperatures include, for example, 370 to 420 F. when the yarn is nylon and 250 to 300 F. for polyester (e.g. polyethylene terephthalate).

Roll 8 may also be separately heated if desired. However, it has been found that due to the normal transfer of heat which takes place from the heated hard metal cylinder to the yarn and from thence to the softer cylinder, it is not necessary in the actual practice of this invention to have both cylinders separately heated. Under some conditions, this is highly beneficial as it permits a much larger variety of substances to be used in the construction of the softer cylinder including those which are generally considered to be poor conductors of heat, such as wood, plastic, rubber or the like. Additional advantages are that the single heat source permits savings in both the construction of the equipment and the power required to maintain the desired operating heat level.

The crimped yarn, after passing through rolls 6 and 8 is allowed to cool, before it is collected on beam 12, in order to set the crimp in the yarn. The yarn is collected by passing the same around a tension roll or bar 13 and then onto beam 12. Tension on the yarn between the rolls and bar 13 should be sufficiently low to avoid pulling out the crimp before the yarn is cooled and the crimp is set. Usually, the tension at this point will vary from 0.05 to 0.1 gram per denier. Higher tension (e.g. 0.15 to 0.25 g.p.d.) may be used between bar 13 and beam 12 to collect the yarn on the beam.

Any multifilament yarn which is thermoplastic and consequently capable of being permanently deformed under conditions of heat and pressure can be processed according to the invention, This includes, for example, nylon, polyester, acetate (such as bi-acetate, tri-acetate), acrylics and the like. The number of filaments making up these yarns can be widely varied but, for optimum results, the yarns used should contain at least 7 filaments up to, for example 68 filaments or even more. Twist in the yarn should be relatively low, e.g. not significantly in excess of 2.5 to 3.0 turns per inch down to just enough twist to hold the yarn filaments together (such as 0.100.25 turns per inch).

FIGURE 2 illustrates the product obtained by the process described above. As shown, the yarn 4, which is made up of the separate filaments 14, is characterized -by a series of permanent, substantially uniform, sinuous bends 16 extending the length of the yarn and another series of permanent but irregularly spaced, non-uniform, minute lateral filament convolutions or loops 18 located on both sides of the central axis of the yarn and essentially perpendicular to the bends 16. These lateral convolutions or loops 18 are formed :by single filament migration which results from the squeezing action of the softer roll on the yarn when the pressure conditions of the invention are employed. As noted earlier, the pressure exerted by the rolls on the yarn should amount to a minimum of at least 800 pounds per lineal inch of the rolls at the point where the rolls contact the yarn. The significance of this pressure limitation is emphasized by the fact that yarn so processed is characterized by a substantially increased cover factor or covering power whereas yarn similarly processed but using lower roll pressure on the yarn shows no appreciable increase in covering power.

It will be appreciated that the number of bends 16 and lateral loops 18 can be widely varied. Advantageously, however, there maybe from 50 to bends 16 and 100 to 300 loops 18 per inch of yarn (untensioned condition) but the number of bends and/or loops may fall outside these ranges.

FIGURE 3 illustrates one way of using theprocessed yarn sheet obtained by the process of FIGURE 1. Thus, for example, upper and lower beams 20 and 22 with the processed yarn 4 thereon are used to simultaneously feed multiple ends of the yarn into a knitting or weaving apparatus 24 adapted to handle multiple ends, such as a warp knitting machine used to make tricot textured fabric. As shown, the yarn is passed from beams 20 and 22 around yarn guide 26 into the fabricating apparatus in conventional fashion, e.g. as disclosed in US. Patent 3,096,559. It will be recognized that the yarn as actually fed into the fabricating machine 24 and knit or woven therein is under sufiicient tension to straighten out the loops and bends in the yarn. However, these loops and bends are permanently set in the yarn and return when the yarn is released from tension, with or without heat or liquid treatment, after the fabric is knit or woven.

It will be appreciated from the foregoing description that the present invention differs uniquely from prior gear crimping procedures in that it not only creates a permanent linear deformation in the yarn but, in addi tion, provides for appreciable axial displacement of the individual filaments therein for lateral loops or distortions which result in a greatly increased covering power for the yarn when knit or woven into textile structures.

While the invention has been described in detail above in connection with the simultaneous crimping of multiple yarn ends or a yarn sheet, the inventive concepts herein can be employed for the processing of individual ends of multifilament yarn. Additionally, the processed end or ends can be employed in a variety of ways other than those mentioned above, for example, in the perparation of knitted products using circular knitting machines or Woven goods where the yarn constitutes the filling and/or Warp, etc. The crimping rolls may take various forms as indicated above including, for example, a Scheiner calender as the top roll with a cooperating rubber cylinder or the like as the bottom roll.

The scope of the invention is defined in the following claims wherein:

I claim:

1. A process for crimping thermoplastic multifilament yarn and for increasing the cover factor and luster of said yarn which comprises passing said yarn between a pair of crimping rolls, one of which is hard and heated to a crimping temperature and the other is composed of a substantially softer, yieldable material and crimping the yarn between the rolls at a pressure of at least 800 pounds per lineal inch to provide a yarn having a series of permanent, non-uniform, lateral loops irregularly spaced along, and on both sides of, a central, substantially uniform, sinuous axis extending longitudinally of said yarn.

2. The process if claim 1 wherein the yarn comprises nylon fibers and the hard roll temperature is between 370 and 420 F.

3. The process of claim 1 wherein the yarn comprises polyester fibers and the hard roll temperature is between 250 and 300 F.

4. The process of claim 1 wherein a plurality of yarns in the form of a warp sheet is simultaneously passed between said rolls and crimped.

5. The process of claim 4 wherein the yarn, after passage through the rolls, is cooled and then collected.

6. The process of claim 1 wherein only the hard roll is heated to crimping temperature and the pressure ex- 5 erted by the rolls on the yarn is between 800 and 2,000 pounds per lineal inch.

7. The process of claim 6 wherein the hard roll is a metal roll and the other roll comprises rubber.

8. The process of claim 6 wherein the hard roll is a 5 metal roll and the other roll comprises a compacted or resin impregnated fibrous substance.

9. The process of claim 8 wherein multiple ends of continuous multifilament yarn are passed through the rolls in the form of a yarn sheet and the collected ends 10 are used for Warp knitting.

6 References Cited UNITED STATES PATENTS 2/1954 Laros 28-72 2/1962 Nijkamp et a1. 161-173 ROBERT F. BURNETT, Primary Examiner.

J. D. FOSTER, Assistant Examiner.

US. Cl. X.R. 

